Light concentration using hetero-junctions of anisotropic low permittivity metamaterials

Focusing incident power into an area of high concentration is of significant interest for various applications. In optics, this has been traditionally achieved with lenses where a higher curvature and lens permittivity typically result in shorter focal distances (low f/D). In this work, we present designs and techniques for collecting, refracting and guiding incident light into an area of high power concentration (a hot spot) at extremely short distances. Specifically, a flat low-profile focusing mechanism is presented using a hetero-junction of anisotropic metamaterials (MTMs). The hetero-junction is formed from two cleaved finite slabs of low (near zero) permittivity anisotropic MTMs with rotated optical axes. The MTMs have near zero longitudinal permittivity while matched in the transverse direction. Such MTMs are shown to provide a unique ability to bend the transverse magnetic or p-polarized light away from the normal and along the interface, contrary to conventional dielectrics, and with minimal reflections; hence allowing for a low profile design. Realizations in the optical regime are presented using periodic bilayers of metal and dielectric. The proposed hetero-junction focusing device concentrates the normally incident plane wave and/or beam into a corresponding focal region similar to a lens via multiple refractions. The hetero-junction is capable of creating a hot spot very close to the device, much closer than dielectric lenses and it significantly outperforms the size requirements of thick high curvature lenses with low f/D ratios. The proposed designs can find applications in various scenarios including solar and thermo photovoltaics, photodetectors, concentrated photovoltaics, non-imaging optics, micro-and nano-Fresnel lenses.